Reflux gas compressor

ABSTRACT

A positive displacement, transverse flow, internally refluxing, rotary gas compressor which operates on a constant volume, variable mass, near-isothermal compression cycle. The compressor includes a pair of involutely lobed, intermeshed impellers that sweep gas from an intake port through the compressor housing to a discharge port in constant volume displacement cavities that are defined by the lobes of the impellers and the compressor housing walls. The cavities are effectively sealed against both the intake and discharge ports over upstream interior housing sidewall portions that extend from the intake port over an angle at least as great as the angle between adjacent lobes of the impellers. Downstream therefrom the interior housing sidewalls are spaced radially from the rotating impellers so as to allow limited reflux counterflow of discharge gas back into the advancing displacement cavities. The refluxing gas isentropically expands into the constant volume displacement cavities so that the pressure of the gas contained in the displacement cavities approaches that of discharge. The final pressure increase with accompanying volume reduction into discharge is gained by adiabatic compression at a low pressure ratio as each cavity opens into discharge. The resulting process is noncontaminating and more energy efficient than compression by volume reduction alone.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to mechanical gas compressors andpumps. More particularly, the present invention is related to positivedisplacement rotary compressors, specifically including those known asRoots blowers.

2. Description of Related Art Including Information Disclosed Under37CFR 1.97-1.99

The present invention is related to the rotary gas compressors disclosedand claimed in the applicant's previously issued U.S. Pat. Nos.4,859,158, 5,090,879, 5,439,358, and 6,312,300, issued Aug. 22, 1989,Feb. 25, 1992, Aug. 8, 1995, and Nov. 6, 2001, respectively.

The class of positive displacement compressors known as Roots blowershas been known to and has served industry continuously since the mid1850's. Roots blowers typically include two lobed impellers, also calledrotors, which are rotated about parallel drive shafts in oppositedirections and which are meshed with one another in a phasedrelationship by means of timing gears attached to each drive shaft.Commercially available Roots blowers typically have impellers with twoor three lobes, but have also been designed to incorporate four or morelobes. Roots blowers having two lobes on each impeller have the greatestvolumetric capacity per revolution and are the most common, asvolumetric capacity is reduced proportionately by adding additionallobes. Roots blowers are particularly useful for moving large volumes ofair or other gases from one volumetric space to another, typicallyagainst low pressure differentials. They are commonly referred to asblowers, as opposed to compressors, because compression of gas does nottake place within the machine itself, as in a typical reciprocatingpiston-and-cylinder compressor; but rather takes place only when gas isdischarged into a volumetric space that is at a higher pressure than thepressure of the intake gas.

Previously known Roots blowers are useful as compressors for compressinggases from atmospheric pressure up to approximately 5 to 7 psigdischarge pressure. They are also useful for evacuation of gas from onevolumetric space to another, and may be used as a vacuum pump or avacuum booster.

Roots blowers offer a number of advantages over other types of gascompressors, including conventional reciprocating piston compressors,helical screw compressors, fan type blowers, and centrifugalcompressors. Among the advantages are simplicity, ruggedness, highvolumetric capacity, and trouble-free operation. Roots blowers areparticularly useful for sweeping large amounts of gas from one space toanother in situations where mixture of intake gas and discharge gas mustbe prevented, as there is little or no backflow or mixture of dischargegas with intake gas, either when the blower is operating or when it isstopped. Further, Roots blowers do not contaminate a gas beingprocessed, as there are no valves or reciprocating, rubbing, orcontacting parts in the flow stream, and lubrication of the impellers isnot ordinarily necessary. The Roots blower also maintains constantdisplacement volume from intake through to discharge, a design featurenot found in any other type of positive displacement compressor.

Roots blowers have not been previously known as being particularlyuseful for compressing a gas against a substantial pressuredifferential. This limitation has been due to heating effects thataccompany such compression. As a gas is impelled through a conventionalRoots blower it is compressed and undergoes an increase in temperatureas it is discharged into a volume of higher pressure discharge gas. Suchcompression is adiabatic, such that the temperature of the gas increasesexponentially with increasing pressure ratios. In addition, heat isgenerated from dynamic flow effects as discharge pressure gas surgesinto impeller cavities and is then expelled in the opposite direction.

This increase in temperature of the gas being processed through theblower leads to heating of the impellers, the housing and othermechanical parts of the blower. Such heating is not uniform throughoutthe compressor and cannot be easily controlled. The compressor housing,for example, can be externally cooled by a number of conventionalmethods, such as the use of water jackets, radiating fins, heat sinks,and the like. The greatest heating problem lies with the impellersbecause there is no practical way to directly cool them. Overheating ofthe impellers leads to their distortion, expansion and eventual bindingagainst the housing. At pressure ratios above about two to one (2:1)such effects become a significant problem and essentially limit thesustained operation of the blower. Overheating of the blower can resultin lockup or other mechanical failure of the impellers and associatedseals and other components, causing extensive damage and shutdown.Overheating has been a major limitation on the use of Roots blowers forcompressing gas against high pressure differentials.

A significant advance in the art was the development of recirculationcycles to effect a moderate reduction in the heating of Rootscompressors. In a recirculating Roots compressor, a portion of thedischarge gas, which is compressed to a higher pressure than the intakegas, is recirculated back into the compressor so as to effectivelyincrease the pressure of gas being processed through the compressor. Insome recirculating compressors a portion of the discharge gas is cooledprior to being recirculated back into the compressor. In both cases theoperating temperature of the compressor is effectively reduced, therebymitigating the heating problems noted above. By this means, a capabilityfor sustained operation has been obtained in some cases up to pressuredifferentials of approximately 2.7:1.

U.S. Pat. No. 2,489,887 to Houghton, for example, discloses the generalconcept of cooling a Roots compressor by introducing recirculated gas ofa lower temperature into the intake gas to reduce heating of thecompressor passages which allow a portion of the high pressure dischargegas to be recirculated back into the pump.

U.S. Pat. No. 3,351,227 to Weatherston discloses a multi-lobed Rootstype compressor having feed-back passages which allow a portion of thehigh-pressure discharge gas to be recirculated back into the pumphousing. Weatherston, however, discloses only the use of quite smallfeedback passages, the size of which are not related to the sizes of theintake and discharge ducts. This results in uneven flow velocities andpressures. As a result, the Weatherston compressor does notsignificantly mitigate overheating of the process gas.

German Patent No. 2,027,272 to Kruger discloses the concept of coolingand recirculating discharge gas in a two-lobed Roots compressor. Thecompressor of Kruger, due to its two-lobed configuration, has noprovision for preventing communication and backflow from the dischargeport into the recirculation ports.

French Patent No. 778,361 to Bucher discloses four-lobed Rootscompressors having recirculation ports. The recirculation ports arehowever small, with the intended purpose of using small, nozzle-likeports to allow the recirculated gas to cool upon entry into thecompressor housing.

U.S. Pat. No. 4,390,331 to Zimmerly discloses a lobed-impeller, positivedisplacement rotary pump that is designed primarily for pumping liquids,with no provision for recirculation.

U.S. Pat. No. 4,390,331 to Nachtrieb discloses a rotary compressorhaving four-lobed impellers, but likewise with no provision forrecirculation.

U.S. Pat. No. 2,906,448 to Lorenz discloses a positive displacementrotary compressor having two-lobed impeller, with a double-walledhousing construction for cooling purposes.

British Patent No. 282,752 to Kozousek discloses a rotary pump that ischaracterized by rotor lobes that are particularly shaped so as toprovide the maximum possible working space or displacement volume perrevolution, and thereby maximize the volumetric capacity of the pump.The pump disclosed in Kozousek discloses small recirculation ports whichare for the purpose of obtaining even delivery of the gas.

In some prior art recirculating Roots compressors, such as thecompressor described in Houghton, the flow of recirculating gas isperiodically interrupted each time a rotor lobe passes the recirculationentry port, or is halted or possibly reversed as a displacement cavityis simultaneously opened to a recirculation entry port and the dischargeport. This results in a loss of momentum and flow of the recirculationfluid, creating heat and reducing the efficiency of the recirculationfluid in cooling the compressor flow. This problem, which is inherent inmany previously known recirculating Roots compressors, is overcome inthe present invention and overcome in the previously issued U.S. Pat.Nos. 5,439,358 and 6,312,300 to Weinbrecht, as will be apparent from thedescription set forth below.

In the applicant's previously issued U.S. patents cited above, certainaspects are disclosed which achieve a substantial change in thethermodynamic nature of the compression cycle, such that the resultingcompression process is significantly more isothermal than adiabatic, andsuch that heat generated in the process is reduced.

Accordingly, it is an object and purpose of the present invention toprovide an improved positive displacement, transverse flow, rotary gascompressor.

It is also an object and purpose of the present invention to provide apositive displacement, transverse flow, rotary gas compressor having animproved gas recirculation or refluxing means for reducing heating ofthe compressor.

It is a further object and purpose of the present invention to provide apositive displacement, transverse flow, rotary gas compressor that ischaracterized by having an internal peripheral counter flow of refluxinggas which flows back from discharge into advancing positive displacementcavities.

It is also an object and purpose of the present invention to provide arotary, positive displacement, transverse flow gas compressor thatproduces significantly less heat inside the compressor, and is thuscapable of operating at higher sustained pressure ratios than havepreviously been attainable.

It is also an objective and purpose of the present invention to providea rotary, positive displacement, transverse flow gas compressor whichestablishes a compression cycle having a thermodynamic nature that issignificantly closer to isothermal than to adiabatic, and that does notrequire internal cooling for operation at pressure ratios of up toapproximately five to one (5:1).

It is also an objective and purpose of the present invention to providea rotary, positive displacement, transverse flow gas compressor whichachieves improved efficiency through a substantially isothermalthermodynamic compression cycle.

It is yet another object and purpose of the present invention to providea rotary, positive displacement, transverse flow gas compressor which ischaracterized by having a means of refluxing internal to the rotorhousing, thereby significantly reducing the amount of fabrication effortand material required for compressor housing production.

SUMMARY OF THE INVENTION

The compressor of the present invention includes a housing havingopposing end walls and mutually opposing interior sidewalls. Thecompressor includes a pair of intermeshed, involutely lobed impellers,also referred to as rotors, which are rotatably journalled in thehousing. The impellers are driven to rotate in opposite directions so asto sweep a gas from intake through the housing from an intake port to adischarge port. The impellers may have from four to nine lobes. Thevolumetric spaces defined by adjacent lobes of the impellers, theopposing end walls of the housing, and the interior sidewalls of thehousing are referred to herein as displacement cavities, in whichparcels of gas are transported from the intake port of the compressor tothe discharge port.

Upstream sidewall portions of the interior housing sidewalls arecylindrically curved, with a radius of curvature as close to the radiiof the rotating impeller lobes as can be achieved within normalmachining tolerances while avoiding sliding contact between the impellerlobes and said upstream sidewall portions, so as to form a substantiallygas-tight seal between the tips of the lobes and the upstream sidewallportions in the manner of a conventional Roots blower.

The upstream sidewall portions of each sidewall extend from the intakeport over an angular sector at least equal to the angular sector betweenadjacent lobes of the impeller, which for example in the case of asix-lobed impeller is 60 degrees, so as to impede or restrict backflowof gas into the intake port. In the preferred embodiment thecylindrically curved upstream sidewall portions of the interiorsidewalls each extend through an angular sector equal to approximatelytwice the angular sector between adjacent lobes of the impellers.

The interior housing sidewalls further include downstream sidewallportions, which are spaced radially from the outer ends of the impellerlobes so as to allow limited peripheral counterflow, or reflux, of thecompressed discharge gas back into the displacement cavities formedbetween adjacent lobes of the impellers. The downstream sidewallportions extend over an angular sector, extending upstream from thedischarge port, of at least the angle between adjacent lobes of theimpellers, which in the case of a six-lobed impeller is 60 degrees.

In the preferred embodiment the upstream sidewall portions of thesidewalls each extend over an angular sector that begins at the intakeport and is approximately equal in magnitude to the angular sector overwhich any two adjacent lobes of the impeller extend, or 120 degrees inthe case of a six-lobed impeller. The downstream sidewall portionsextend upstream from the discharge port over an angular sector alsoapproximately equal to the angular sector represented by any twoadjacent lobes of the impeller, or 120 degrees in the case of thesix-lobed impeller.

The reflux discharge gas that is admitted into the displacement cavitiesby peripheral backflow along the downstream wall portions of thesidewalls serves to raise the pressure of intake gas within thedisplacement cavities, so that the gas pressure within each displacementcavity is nearly equal to that of the discharge pressure as thecontained gas is swept into the discharge port.

In the preferred embodiment the impellers each have six lobes, and theupstream and downstream portions of the interior housing sidewalls eachextend over a combined angular sector of approximately 300 degrees, withthe upstream wall portions each extending through an angular sector ofapproximately 120 degrees. This embodiment is preferred because itresults in slippage or backfill flow between the tips of the impellerlobes and the interior housing sidewalls being collected in a followingcavity and carried forward into discharge, and is thereby characterizedby improved volumetric efficiency.

The compressor of the present invention is useful in applicationsrequiring the continuous compression of large volumes of gas or vapor.The transverse flow arrangement and the rugged design permit in-linemultiple staging driven by a single power source, so that very highcompression system pressure ratios can be achieved. The near-isothermalthermodynamic nature of the compression process provides an inherentenergy efficiency advantage of from 8% to 14% when compared to any priorart method of compression.

These and other aspects of the present invention will become moreapparent upon consideration of the detailed description of the inventionset forth below and in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is incorporated into and a part of thisspecification and, when taken in combination with the detaileddescription below, illustrates the operation and construction of thebest mode of the invention known to the inventor.

FIG. 1 is an end view in cross section of the preferred embodiment ofthe rotary compressor of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is illustrated a preferred embodiment of thepositive displacement, transverse flow, rotary compressor 10 of thepresent invention. The compressor 10 includes two involutely lobedimpellers 12 and 14, each having six lobes, which are rotatablyjournalled within a hollow housing 16 and which are driven in oppositerotational directions as indicated by the directional arrows in FIG. 1.Impellers 12 and 14 are shaped and intermeshed with one another so as toform a substantially gas-tight seal that prevents gas from passingbetween them at all stages of their rotation. In operation, gas is drawninto the compressor 10 through an intake port 18 and is discharged froma discharge port 20 at the opposite side of the compressor 10. Forreasons that will be apparent below, it is noted that the individuallobes of the six-lobed impellers 12 and 14 are spaced at 60 degreeangular intervals from one another.

The housing 16 has interior surfaces which include two opposing,parallel, planar end walls (only one end wall 22 of which is shown),each of which are orthogonal to the axes of rotation of the impellers 12and 14.

Housing 16 further includes upper and lower opposing interior sidewalls24 and 26, respectively, which each extend from the intake port 18 tothe discharge port 20 across the upper and lower halves of the housing16, respectively. The volumetric spaces defined by adjacent lobes of theimpellers 12 and 14, the opposing end walls of the housing, and theinterior sidewalls 24 and 26 of the housing 16 are referred to herein asdisplacement cavities, in which parcels of gas are transported from theintake port 18 of the compressor to the discharge port 20.

As described in more detail below, the sidewalls 24 and 26 includeupstream and downstream sidewall portions of slightly different sizesand shapes, which function to permit a limited amount of reflux backflowof high pressure discharge gas into the compressor 10 during transportof gas through the compressor 10, while nevertheless preventing backflowof discharge gas into the intake port 18.

Specifically, the upper interior sidewall 24 includes an upstreamsidewall portion 24 a and a downstream sidewall portion 24 b, which areseparated by a short transition sidewall portion 24 c.

The upstream sidewall portion 24 a is cylindrically curved and has aradii of curvature that is as close to the maximum radii of the lobes ofimpeller 12 as can be achieved within normal machining tolerances, whileavoiding frictional contact between the tips of the lobes of impeller 12and the upstream sidewall portion 24 a. The impeller 12 and the upstreamsidewall portion 24 a, taken alone, thus function in the manner of aconventional Roots compressor to sweep parcels of gas from the intakeport 18 into the compressor 10, while preventing backflow of gas intothe intake 18. The upstream sidewall portion 24 a extends over anangular sector, as measured from the upper edge of the intake port 18,of approximately 120 degrees, or the angular sector defined by any twolobes of the six-lobed impeller 12.

The downstream sidewall portion 24 b is at all points at a greaterdistance from the axis of rotation of impeller 12 than is the upstreamsidewall portion 24 a. More specifically, in the preferred embodimentthe downstream sidewall portion 24 b has a noncylindrical curvature thatis characterized by a slightly but progressively increasing distancefrom the axis of rotation of impeller 12, as measured moving from theupper lip of discharge port 20 toward the transition sidewall portion 24c; such that the backflow reflux of discharge gas past the tips of thelobes of impeller 12 diminishes at greater distances upstream from thedischarge port 20.

Generally, the greater radial distance of the downstream sidewallportion 24 b from the axis of rotation of the impeller 12, as comparedwith that of the upstream sidewall portion 24 a which effectively formsa gas-tight seal with the tips of the impeller lobes, allows acontrolled and limited amount of high pressure discharge gas to flowback into the displacement cavities that are bounded by downstreamsidewall portion 24 b, before they open into the discharge port 20. Morespecifically, the progressively increasing distance between the surfaceof the downstream sidewall portion 24 b and the impeller axis ofrotation, as measured moving toward the discharge port 20, allows for agreater amounts of high pressure discharge gas to flow into thedisplacement cavity nearest the discharge port 20, while allowing alesser amount of discharge gas to flow into the immediately precedingdisplacement cavity, and an even lesser amount to flow into the nextpreceding displacement cavity. As shown in FIG. 1, limited andprogressively decreasing amounts of high pressure discharge gas areallow to backflow into the three displacement cavities located upstreamfrom the discharge port 20, while at all times the displacement cavityor cavities nearest the intake port 18, that is, any displacement cavitybounded by the upstream sidewall portion 24 a, is effectively sealed andthus does not permit backflow of high pressure discharge gas into suchcavity or into the intake port 18. As will be further seen from FIG. 1,as any lobe of the impeller 12 passes the transition sidewall portion 24c, which merely represents a transition in the machined interiorsidewall 24 of the housing 16, higher pressure discharge gas isprogressively and increasingly admitted past the tip of the lobe so asto increase the pressure in the preceding displacement cavity, such thatby the time the displacement cavity is opened to the discharge port 20the pressure in the displacement cavity is substantially increased,thereby reducing the increase in temperature occasioned by opening ofthe displacement cavity into the discharge port 20.

The upper sidewall portions 24 a, 24 b and 24 c of the illustratedpreferred embodiment, combined, extend over an angular sector ofsomewhat less than 270 degrees, as measured from the upper edge of theintake port 18 and extending across the upper side of the housing 16 tothe upper edge of the discharge port 20.

The lower interior sidewall 26 includes an upstream sidewall portion 26a, a downstream sidewall portion 26 b, and a short transition sidewall26 c, all of which function in the same manner as the correspondingportions of upper sidewall 24, to admit limited amounts of high pressuredischarge gas to pass by the tips of the lobes of impeller 14 andthereby increase the pressure in the displacement cavities before theyopen into the discharge port 20, yet without allowing backflow of highpressure discharge gas into the intake port 18.

The lower sidewall portions 26 a, 26 b and 26 c likewise extend togetherover an angular sector of somewhat less than 300 degrees, as measuredfrom the lower edge of the intake port 18 to the lower edge of thedischarge port 20. In this regard, it will be noted that in thepreferred embodiment the size of the intake port 18 is larger than thesize of the discharge port 20, which is a consequence of the gas beingdischarged from the discharge port 20 being at a higher pressure andlower volume than the gas drawn into the intake port 18.

From the intake port 18, the upper and lower cylindrically curvedupstream sidewall portions 24 a and 26 a each extend, in the illustratedpreferred embodiment, over an angular sector of approximately 128degrees, which angular sector is slightly greater than the anglespanning two displacement cavities between any two successive pairs oflobes of the six-lobe rotors 12 and 14. Over this sector the sidewallportions 24 a and 26 a have a substantially cylindrical curvature, witha preferable tolerance of not more than two one thousandths of an inchbetween the outside lobe tips of the impellers 12 and 14 and thecylindrical surfaces of the sidewall portions 24 a and 26 a.

In contrast, the surfaces of the upper and lower downstream sidewallportions 24 b and 26 b of the housing 16 are at a greater distance fromthe axes of the impellers 12 and 14 than are the surfaces of thesidewall portions 24 a and 26 a, so as to provide a controlled clearancebetween the tips of the impeller lobes and the surfaces of sidewallportions 24 b and 26 b, in order to allow controlled amounts of internalreflux counterflow of high pressure discharge gas back into thedisplacement cavities between the lobes of the impellers 12 and 14.

It should also be recognized that, in accordance with the invention, theupstream sidewall portions 24 a and 26 a need only span an angularsector of at least 60 degrees in order to avoid any backflow ofcompressed discharge gas back into the intake port 18, while stillallowing controlled reflux counterflow of compressed discharge gas intothe displacement cavities formed between adjacent lobes of each rotor 12and 14. Conversely, the upper and lower downstream sidewall portions 24b and 26 b need only span an angular sector of at least 60 degrees fromthe upper and lower lips of the discharge port 20, respectively, inorder to allow controlled reflux counterflow of compressed discharge gasback into at least one displacement cavity before it opens into thedischarge port 20.

In the illustrated preferred embodiment, the transition sidewallportions 24 c and 26 c are centered at approximately the midpointbetween the lips of the intake and discharge ports 18 and 20, orapproximately 128 degrees from each of the upper and lowers lips of theports 18 and 20, such that the angular sectors of the upstream sidewallportions 24 a and 26 a and the angular sectors of downstream sidewallportions 24 b and 26 b are approximately the same, i.e. approximately128 degrees.

As noted, the surfaces of upstream sidewall portions 24 a and 26 a areessentially cylindrical so as to prevent backflow of compressed gas intothe intake port 18. However, the surfaces of downstream sidewallportions 24 b and 26 b may be cylindrical, or may be of progressivelyincreasing diameter from the axes of rotation of the impellers 12 and14, as in the preferred embodiment. Depending on the level of refluxcounterflow of compressed discharge gas desired at various points alongthe downstream sidewall portions 24 b and 26 b, the sidewall portions 24b and 26 b may be cylindrical along nearly their entire span, or theymay be of progressively increasing radius toward the discharge port 20.Further, the transition sidewall portions 24 c and 26 c may be eitherabrupt, or gradual as illustrated in FIG. 1.

The lobed impellers 12 and 14 are essentially identical to one another,and their function during the operation of the compressor is asdescribed further below. The six lobes of each of the impellers 12 and14 are substantially identical to one another. In rotation, the lobes ofimpellers 12 and 14 intermesh in close contact with one another so thatthere is at all times a high impedance clearance between the impellers,which clearance is small in comparison with the volumetric displacementof the compressor, and which essentially restricts by sonic chokingbackflow of high pressure discharge gas through to the intake region.

Briefly, the impellers 12 and 14 are driven to rotate in oppositedirections about their parallel axes of rotation. The axes of theimpellers are also collinear with the central longitudinal axes of thecylindrically curved interior sidewall portions 24 a and 26 a,respectively. The impellers 12 and 14 are maintained in proper angularrelationship to one another, which is at an angular phase relationshipof 30 degrees with respect to one another, by their normal intermeshingrelationship, and also by means of timing gears (not shown), which arelocated outside of the primary chamber of the housing 16.

In operation, gas is admitted to the compressor through the intake port18 that is generally centered between the upper and lower side wall 24and 26. Individual parcels of gas are swept through the housing 16 bythe impellers 12 and 14, with each parcel occupying a displacementcavity which is defined by a pair of adjacent impeller lobes and by theinterior walls of the compressor housing 16. So long as the leading lobeof a displacement cavity is positioned adjacent sidewall portion 24 a or26 a, the parcel of gas remains at the intake pressure. As soon as theleading lobe of the displacement cavity reaches sidewall portion 24 b or26 b, a limited amount of higher pressure discharge gas begins flowinginto the displacement cavity. Depending on the precise shape, sectorspan, and radii of the downstream sidewall portions 24 b and 26 b atvarious points along their surfaces, the rate and amount of refluxcounterflow of compressed discharge gas back into the displacementcavity may be vary as the displacement cavity travels through thehousing 16. By the time the displacement cavity opens into the dischargeport 20, the pressure of the parcel of gas is increased, up to as muchas the pressure of the gas in the discharge port 20, and the gas is thusswept into of the discharge port 20 with little or no adiabaticcompression and associated heating.

It is believed that compressor of the present invention will findutility in serving a wide variety of applications where high volume,sustained operation is required at single stage pressure ratios of up tofive to one (5:1). Inasmuch as Roots type compressors have heretoforeonly been capable of sustained operation at pressure ratios notexceeding approximately two to one (2:1) due to limitations imposed byoverheating of the compressor components, the higher attainable pressureratio capability of the present invention makes it useful inapplications not previously considered feasible.

It will be appreciated that the temperature of the gas being processedis sufficiently reduced by the reflux counterflow of discharge gas thatmeans of heat removal are not ordinarily required, either internal orexternal, and problems associated with overheating and thermaldistortion are reduced. The compressor is characterized by having a moreuniform process temperature, so that temperature differences in thetransverse flow direction from intake to discharge do not cause thermaldistortion difficulties. As a consequence of the substantiallyisothermal nature of the compression cycle, the reflux compressor has aninherent energy efficiency advantage when compared with othercompression processes, an advantage that improves with increasingpressure ratios.

Although the present invention is described herein with reference to apreferred embodiment, it will be understood that various modifications,substitutions and alterations, which may be apparent to one of ordinaryskill in the art, may be made without departing from the essence of thepresent invention. Accordingly, the present invention is described bythe following claims.

1. A positive displacement, transverse flow, internally refluxing rotarygas compressor comprising: a housing having two opposing end walls andtwo mutually opposing interior sidewalls, said housing including a gasintake port between said interior side walls at one end of said housingand a gas discharge port between said interior sidewalls at the oppositeend of said housing from said intake port; first and second involutelylobed impellers journalled within said housing for rotation in oppositedirections about parallel axes of rotation extending transversely fromsaid end walls, said impellers being spaced from and intermeshed withone another so as to form a high impedance gas seal between saidimpellers while said impellers are rotated in opposite directions, andeach of said impellers having from four to nine radially extending lobesthat are equally spaced angularly with respect to one another and whichthereby define an angular sector between adjacent lobes, and withadjacent lobes of said impellers and said end walls and said interiorsidewalls of said housing together defining displacement cavities inwhich parcels of intake gas are swept through said housing from saidintake port to said discharge port; said opposing interior sidewallseach having an upstream sidewall portion and a downstream sidewallportion, said upstream sidewall portions being substantially cylindricaland having cylindrical axes that are coaxial with the respective axes ofrotation of said impellers, said upstream sidewall portions having radiiof curvature sized so as to form an effective gas seal with said lobesof said impellers and thereby prevent significant backflow of compresseddischarge gas while also allowing said lobes to sweep gas through saidhousing, and said upstream sidewall portions extending from said intakeport over an angular sector at least as great as said angular sectorbetween adjacent lobes of said impellers; and said downstream sidewallportions of said opposing interior sidewalls extending upstream fromsaid discharge port over an angular sector at least as great as saidangular sector between adjacent lobes of said impellers, and being sizedradially so as to allow a controlled amount of reflux counterflow ofcompressed discharge gas into the displacement cavities formed betweenadjacent lobes of said impellers by controlled flow of compresseddischarge gas between said lobes of said impellers and said downstreamsidewall portions of said housing.
 2. The positive displacement,transverse flow, internally refluxing, rotary gas compressor defined inclaim 1 wherein each of said involutely lobed impellers has four lobes,and wherein said upstream sidewall portions extend over an angularsector of at least approximately ninety degrees downstream from saidintake port.
 3. The positive displacement, transverse flow, internallyrefluxing, rotary gas compressor defined in claim 1 wherein each of saidinvolutely lobed impellers has five lobes, and wherein said upstreamsidewall portions extend over an angular sector of at leastapproximately seventy two degrees downstream from said intake port. 4.The positive displacement, transverse flow, internally refluxing, rotarygas compressor defined in claim 1 wherein each of said involutely lobedimpellers has six lobes and wherein said upstream sidewall portionsextend over an angular sector of at least approximately sixty degreesdownstream from said intake port.
 5. The positive displacement,transverse flow, internally refluxing, rotary gas compressor defined inclaim 1 wherein each of said involutely lobed impellers has seven lobesand wherein said upstream sidewall portions extend over an angularsector of at least approximately fifty two degrees downstream from saidintake port.
 6. The positive displacement, transverse flow, internallyrefluxing, rotary gas compressor defined in claim 1 wherein each of saidinvolutely lobed impellers has eight lobes and wherein said upstreamsidewall portions extend over an angular sector of at leastapproximately forty five degrees downstream from said intake port. 7.The positive displacement, transverse flow, internally refluxing, rotarygas compressor defined in claim 1 wherein each of said involutely lobedimpellers has nine lobes and wherein said upstream sidewall portionsextend over an angular sector of at least approximately forty degreesdownstream from said intake port.
 8. The positive displacement,transverse flow, internally refluxing, rotary gas compressor defined inclaim 1 wherein said downstream sidewall portions each extend upstreamfrom said discharge port over an angular sector of at least twice theangular sector between adjacent lobes of each of said impellers.
 9. Thepositive displacement, transverse flow, internally refluxing, rotary gascompressor defined in claim 4 wherein said downstream sidewall portionseach extend upstream from said discharge port over an angular sector ofat least one hundred ten degrees.
 10. The positive displacement,transverse flow, internally refluxing, rotary gas compressor defined inclaim 1 wherein said downstream sidewall portions are cylindrical inshape and have a radius of curvature greater than that of said upstreamsidewall portions.
 11. The positive displacement, transverse flow,internally refluxing, rotary gas compressor defined in claim 1 whereinsaid downstream sidewall portions are each of progressively increasingradius with regard to the axes of rotation of said impellers, from saidupstream sidewall portion to said discharge port.
 12. The positivedisplacement, transverse flow, internally refluxing, rotary gascompressor defined in claim 4 wherein said downstream sidewall portionseach extend upstream from said discharge port over an angular sector ofat least one hundred eighty degrees.
 13. The positive displacement,transverse flow, internally refluxing, rotary gas compressor defined inclaim 3 wherein said downstream sidewall portions each extend upstreamfrom said discharge port over an angular sector of at least one hundredforty degrees.
 14. The positive displacement, transverse flow,internally refluxing, rotary gas compressor defined in claim 5 whereinsaid downstream sidewall portions each extend upstream from saiddischarge port over an angular sector of at least one hundred fourdegrees.
 15. The positive displacement, transverse flow, internallyrefluxing, rotary gas compressor defined in claim 6 wherein saiddownstream sidewall portions each extend upstream from said dischargeport over an angular sector of at least ninety degrees.
 16. The positivedisplacement, transverse flow, internally refluxing, rotary gascompressor defined in claim 7 wherein said downstream sidewall portionseach extend upstream from said discharge port over an angular sector ofat least eighty degrees.
 17. The positive displacement, transverse flow,internally refluxing, rotary gas compressor defined in claim 10 furtherincluding a transition sidewall portion between said upstream anddownstream sidewall portions of said interior sidewalls.
 18. Thepositive displacement, transverse flow, internally refluxing, rotary gascompressor defined in claim 11 further including a transition sidewallportion between said upstream and downstream sidewall portions of saidinterior sidewalls.
 19. The positive displacement, transverse flow,internally refluxing, rotary gas compressor defined in claim 12 whereinsaid downstream sidewall portions are each of progressively increasingradius with regard to the axes of rotation of said impellers, from saidupstream sidewall portion to said discharge port.
 20. The positivedisplacement, transverse flow, internally refluxing, rotary gascompressor defined in claim 1 wherein said upstream sidewall portionsextend from said intake port over an angular sector at least twice asgreat as the angular sector between adjacent lobes of said impellers,and wherein said downstream sidewall portions each extend upstream fromsaid discharge port over an angular sector of at least twice the angularsector between adjacent lobes of each of said impellers.